When a 4.5-magnitude earthquake shifted the Hayward Fault earlier this month, Golden Gate Bridge managers jumped into action to determine if there was any damage to the span, part of a “Bridge Earthquake Response Plan.”

Soon after, an inspection was performed by bridge security officers with video cameras, followed by a driving inspection of the road, officials said. In addition, engineers performed a field inspection at the bridge.

“After every earthquake we do a visual inspection,” said John Eberle, deputy district engineer at the Golden Gate Bridge. “We also have a monitoring plan where we do a more in-depth inspection at locations where the bridge may be more susceptible than at other locations. We have monitors on the bridge, which gives us information about what the bridge actually feels after the earthquake. It does depend on the magnitude, but after each earthquake we do go out and investigate it.”

It was determined that there was no damage to the bridge caused by the Jan. 4 earthquake, but in the temblor-prone region the protocol is important.

Last April, bridge staff met with representatives from the California Department of Conservation in Sacramento to discuss upgrades to the district’s equipment to receive data quicker after a seismic event. A follow-up meeting is planned later in the year to discuss upgrades.

“We have a sensor in the sergeants’ office and there is an alarm that is set up in that device,” Eberle said. “If the alarm does not go off, it means the bridge didn’t feel anything. If the alarm does go off, it means the proximity of the earthquake is such that the bridge felt some motion. The sensors tell us what the acceleration was at the bridge.”

There are almost 100 sensors mounted on or near the Golden Gate Bridge and another 85 on the Richmond-San Rafael Bridge, as well as other Marin County buildings, which record movement.

The sensor system is designed to immediately record data and help engineers make the structures better able to absorb future earthquakes.

As part of the program, scientists have placed thousands of sensors around the state to measure how structures and soil react under the stress of Earth movement. The monitoring devices, about the size of cake boxes, measure gravity forces.

The program was established by the state Division of Mines and Geology in 1972 after the 6.4-magnitude San Fernando earthquake in Southern California in which 65 people died.

The sensors did not start to appear on Bay Area bridges until the mid-1990s, after the Oct. 17, 1989, 6.9-magnitude Loma Prieta earthquake.

The value of the sensors is twofold. In the short term, they serve as a warning system providing a wealth of information about the bridge and what type of forces it was exposed to that would be impossible to get with a visual inspection.

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The newer sensors have modems that dial a computer at the survey, where the information is instantaneously collected. From there, maps detailing the quake can be produced rapidly, providing officials with information on which structures might be at risk of damage.

In the long term, the sensor data give engineers an idea of how structures react in an actual earthquake.

The earthquake monitoring devices are installed in a variety of structures such as high-rise buildings, dams, bridges, hospitals and industrial facilities. They are also placed in open land to measure the effects of earthquakes on soil and how energy waves travel.

The sensors are at Marin General Hospital in Greenbrae, Novato Community Hospital and on the Petaluma Bridge on Highway 37, among other local sites.

This month’s earthquake also brought attention to the need to finish seismic work on the Golden Gate Bridge, a cost pegged between $450 million and $500 million.

Presently the bridge is considered safe, with officials saying the north and south ends could sustain an 8.3-scale quake. Seismic work on the center suspension section still needs to be completed. That portion could withstand a large earthquake, bigger than a 7.0, but there would be extensive damage and the bridge would likely have to be closed for a long period.

“We need to be prepared when the big one hits,” said Priya Clemens, bridge spokeswoman.